Ab initio study of the vibrational and electronic properties of CdGa2S4 and CdGa2Se4 under pressure

The vibrational spectra of CdGa2S4 and CdGa2Se4 under pressure were calculated with an ab initio technique and compared to the experimental results of Ursaki et al (Ursaki V V, Burlakov II, Tiginyanu I M, Raptis Y S, Anastassakis E and Anedda A 1999 Phys. Rev. B 59 257). The comparison is good even though the conclusions are different. Ursaki et al concluded that CdGa2S4 and CdGa2Se4 are disordered under pressure while here these materials remained ordered. The pressure dependence of the band gap is calculated to help clarify whether or not the disordering is occurring.